1. Field of the Invention
This invention relates to a thread cutter for a chain stitch sewing machine which performs chain stitch sewing by cooperation of a needle that is driven up and down and a looper that is controlled for rotation in synchronization with the needle. Another invention of the subject application relates to a drive unit for a multi-head sewing machine where a needle bar and a cloth pressing member, arranged in each of a plurality of machine heads, are moved up and down.
2. Description of the Related Art
(Prior art of the first invention)
A conventional thread cutter for a chain stitch sewing machine is disclosed, for example, in Japanese Patent Publication No. HEI 3-11239. This publication discloses a thread cutting mechanism where a sewing thread is cut by cooperation of a movable knife that advances into or retracts from a gap between the under surface of a needle plate and the top surface of a looper and a stationary knife fixed to the under surface of the needle plate. Japanese Unexamined Patent Publication No. HEI 5-239757 discloses another conventional thread cutter, which includes a scissor type cutting mechanism, a thread guiding mechanism for guiding a sewing thread to the cutting mechanism, and a thread holding mechanism for holding the sewing thread after it is cut.
The thread cutter, disclosed in the aforementioned Japanese Patent Publication No. HEI 3-11239, is not equipped with a mechanism for holding the end of the thread remaining on the looper side after it is cut in a predetermined position. For this reason, when a needle is threaded by rotation of the looper at the time of the start sewing operation, the thread end will be moved due to the rotation of the looper. Therefore, tension cannot be applied to the sewing thread and in certain cases the needle cannot be threaded appropriately, and consequently the drawback is pointed out that errors can occur in the start of the sewing operation.
The thread cutter, disclosed in the aforementioned Japanese Unexamined Patent Publication No. HEI 5-239757, is equipped with a mechanism for holding the end of the thread remaining on the looper side after it is cut in a predetermined position. However, because the thread cutter is structurally complicated due to a large number of components, there is the drawback that the production cost is increased and that the operation cannot be performed with reliability.
(Prior art of the second invention)
In multi-head sewing machines, the drive unit for elevating needle bars and cloth pressing members individually arranged in a plurality of machine heads rotates the needle cam and the cloth pressing cam fixed on the main machine shaft, and in association with these rotations, repeats reciprocating movement of the needle bar driving lever and the cloth pressing member driving lever over a constant range, whereby the needle bar and the cloth pressing member are individually moved up and down. When the needle bar and the cloth pressing member are required to be retracted for exchange of a piece of cloth, installed retracting mechanism is operated so that the driving levers are moved upward beyond the constant range, whereby the needle bar and the needle pressing member are retracted to a position beyond the top dead point of the sewing operation.
However, even in the state where the needle bar and the cloth pressing member have been retracted, if the main machine shaft is rotating, the respective driving levers will be interlocked depending upon the rotational positions of the needle bar cam and cloth pressing member. Therefore, in certain cases the needle bar and the cloth pressing member continue their operations although they are in incomplete operations. Therefore, in order to stop an arbitrary machine head of the multi-head sewing machine, it is necessary that the needle bar and cloth pressing member of that machine head be retracted and at the same time the interlocked relationship between the main machine shaft and each cam be cut off by a clutch mechanism. However, because the clutch mechanism has to be arranged in correspondence With the respective machine heads, there is the problem that the drive unit becomes structurally complicated.